1. Field of the Invention
The present invention relates to a radio communication system, a radio base-station apparatus, a mobile radio-station apparatus, a radio-zone assignment method and a radio communication method, all fit for use in mobile data communication, particularly radio transmission of multi-carrier signals.
2. Related Art
Two methods of setting many channels to provide mobile communication service in a larger geographical area are known. They are time division and frequency division. In the time-division method, use-time zones are assigned to cells, respectively, and the base stations must therefore be synchronized. A radio communication system that employs the time-division method is inevitably complex in configuration. In the frequency-division method, specific frequencies are assigned to the cells, respectively, and each base station can use the frequency assigned to it and can be controlled independently of any other base station. Thus, a radio communication system that adopts the frequency-division method is simple in configuration.
FIG. 1 illustrates a conventional base station 120, which is designed to transmit and receive data through the Internet network 12. As FIG. 1 shows, the base station 120 comprises a line controller 121, a central processing unit (CPU) 122, a channel coding/decoding section 123, a modulating/demodulating section 124, a transmitting/receiving section 125, and an antenna 126. The line controller 121 is connected to the Internet network 12, for controlling the line. The controller 121 receives data (IP packets) through the network 12. Each IP packet is supplied to the channel coding/decoding section 123. The section 123 converts the IP packet to data of radio-transmission format. The modulating/demodulating section 124 performs, for example, QPSK modulation on the data. The data thus modulated is supplied to the transmitting/receiving section 125. The section 125 performs transmission processes, such as frequency conversion and amplification, on the data. The data thus processed is transmitted by radio from the antenna 126 to communication terminals.
Any signal transmitted from a communication terminal and detected by the antenna 126 is supplied to the transmitting receiving section 125. The section 125 carries out a reception process, such as frequency conversion, on the signal, converting the signal to data, which is supplied to the modulating/demodulating section 124. The section 124 demodulates the data, which is supplied to the channel coding/decoding section 123. The section 123 decodes the data, thereby generating an IP packet. The IP packet is supplied to the line controller 121 and thence sent to the Internet network 12.
The central processing unit (CPU) 122 controls all processes effected in the base station 120, by using the bus line BL provided in the base station 120. When the base station 120 is installed in a geographical area (cell), it is assigned with a channel specific to the cell. The information representing the channel is stored in the memory incorporated in the line controller 121. The CPU 122 supplies the information to the transmitting/receiving section 125, which stores the information.
FIG. 2 shows a communication terminal 130. As shown in FIG. 2, the terminal 130 comprises an antenna 131, a transmitting/receiving section 132, a modulating/demodulating section 133, a channel coding/decoding section 134, a central processing unit (CPU) 135, a display section 136, and a control section 137. The antenna 131 receives the data transmitted from the base station 120 illustrated in FIG. 1. The transmitting/receiving section 132, which is connected to the antenna 131, effects a reception process, such as frequency conversion, on the data. The data is supplied to the modulating/demodulating section 133. The section 133 demodulates the data, which is supplied to the channel coding/decoding section 134. The section 134 converts the format of data, from radio-transmission format to IP packet format. The data of IP packet format is supplied to the central processing unit (CPU) 135. The CPU 135 processes the data by using an application program, generating data that can be displayed. The data is supplied to the display section 136.
The control section 137 connected to the central processing unit (CPU) 135 generates data (IP packet) to be transmitted to the base station 120. The data is supplied to the channel coding/decoding section 134. The section 134 converts the data to data of radio-transmission format. The radio-transmission format data is supplied to the modulating/demodulating section 133. The section 133 carries out modulation, such as QPSK modulation, on the data. The data, thus modulated, is supplied to the transmitting/receiving section 132. The section 132 performs transmission processes, such as frequency conversion and amplification, on the data. The data thus processed is transmitted by radio from the antenna 131 to the base station 120.
The information representing the channel assigned to the base station 120 is extracted from the control signal transmitted from the base station 120. The CPU 135 supplies the information to the transmitting/receiving section 132. The information is stored in the transmitting/receiving section 132.
Base stations including the base station 120 and communication terminals including the terminal 130 are connected to the Internet network 12, whereby a communication system is constituted. The communication terminal 130 can receive, for example, Internet broadcast programs from various content servers provided on the Internet network 12.
Radio signals to be transmitted between the base station 120 and the communication terminal 130 will be described. This communication system employs a single-carrier radio transmission scheme. In other words, data to be transmitted is modulated with a single carrier that falls within a prescribed channel band, into a radio transmission signal.
FIG. 3 illustrates an example of channel assignment, applied in the communication system. Both the up-link and the down-link are composed of a single carrier each. Eight channels are available. The carrier of each channel is modulated by QPSK modulation or the like. In the communication system, each base station uses one specific channel to achieve data communication with any communication terminal.
In the conventional communications system, the channels may be set by means of frequency division. If so, a frequency is divided into several bands, which are assigned to the cells of the communication system. The system is therefore simple, but the frequency band each cell can use is narrow. This makes it impossible to increase the transmission speed.